Power transfer device having sensor circuit with dual sensors for identifying locking state

ABSTRACT

An apparatus for transferring power includes a sensor circuit for identifying a position of an axially-movable locking element. The axially-movable element is movable between a first position, which inhibits transmission of rotary power through the apparatus, and a second position that permits transmission of rotary power through the apparatus. The sensor circuit includes two Hall-effect sensors that are employed to sense a position of the axially-movable locking element and produce sensor signals that are employed to control a magnitude of the current that is output from the sensor circuit. A method of detecting an operating mode of a power transfer device that is configured to transmit rotary power is also provided.

This application is a continuation of U.S. patent application Ser. No.11/359,907 filed Feb. 22, 2006 (issued as U.S. Pat. No. 7,507,176 onMar. 24, 2009), which is a continuation-in-part of U.S. patentapplication Ser. No. 11/137,997 filed May 26, 2005 (issued as U.S. Pat.No. 7,211,020), the disclosures of which are hereby incorporated byreference as if fully set forth in detail herein in their entirety.

BACKGROUND

The present disclosure generally relates to differentials for motorvehicles and, more particularly, to a power transfer device having asensor circuit with dual sensors for identifying a locking state of thepower transfer device.

As is known, many motor vehicles are equipped with driveline systemsincluding differentials which function to drivingly interconnect aninput shaft and a pair of output shafts. The differential functions totransmit drive torque to the output shafts while permitting speeddifferentiation between the output shafts.

Conventional differentials include a pair of side gears fixed forrotation with the output shafts and two or more sets of meshed piniongears mounted within a differential case. However, the conventionaldifferential mechanism has a deficiency when a vehicle is operated on aslippery surface. When one wheel of the vehicle is on a surface having alow coefficient of friction, most or all of the torque will be deliveredto the slipping wheel. As a result, the vehicle often becomesimmobilized.

To overcome this problem, it is known to provide a mechanicaldifferential having an additional mechanism that limits or selectivelyprevents differentiation of the speed between the output shafts.Typically, the mechanical device used to provide the limited-slip ornon-slip function is a friction clutch. The friction clutch is a passivedevice which limits the differential speed between the output shaftsonly after a certain differential speed has been met. Additionally, suchmechanical devices may not be selectively disengaged during operation ofanti-lock braking systems or vehicle traction control systems. Forexample, four-wheel anti-lock braking systems may attempt to measure andcontrol the rotational speed of each wheel independently. If amechanical type limited slip differential is present, independentcontrol of the speed of each wheel coupled to a differential is nolonger possible. Accordingly, it would be desirable to provide animproved differential which may be actively controlled in conjunctionwith other control systems present on the vehicle. A detection systemoperable to determine the present state of operation of the differentialmay also be desirable.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In one form, the present teachings provide an apparatus for transferringpower. The apparatus includes a first power transmitting element, asecond power transmitting element, a housing, a first locking elementreceived in the housing and coupled to the first power transmittingelement, a second locking element and a sensor circuit. The secondlocking element is received in the housing and coupled to the secondpower transmitting element. The second locking element is axiallymovable along a rotational axis about which the first and second lockingelements are rotatably disposed such that the second locking element ismovable between a first position, in which rotary power is nottransmitted between the first and second locking elements, and a secondposition in which rotary power is transmitted between the first andsecond locking elements. The sensor circuit is disposed in the housingand includes a first Hall-effect sensor and a second Hall-effect sensorthat are configured to sense an axial position of the second lockingelement. The sensor circuit produces a single analog output current thatis indicative of a sensed axial position of the second locking element.

In another form, the present teachings provide a method of detecting anoperating mode of a power transfer device that is configured to transmitrotary power. The power transmitting device has a first powertransmitting element, a second power transmitting element, a housing, afirst locking element received in the housing and coupled to the firstpower transmitting element, a second locking element received in thehousing and coupled to the second power transmitting element, and asensor circuit having first and second Hall-effect sensors and first andsecond switches. The second locking element is axially movable along arotational axis about which the first and second locking elements arerotatably disposed such that the second locking element is movablebetween a first position, in which rotary power is not transmittedbetween the first and second locking elements, and a second position inwhich rotary power is transmitted between the first and second lockingelements. The method includes: fixedly coupling the first and secondHall-effect sensors to one of the second locking element and thehousing; fixedly coupling a magnet to the other one of the secondlocking element and the housing; sensing a position of the secondlocking element with the first Hall-effect sensor and responsivelyproducing a first sensor signal in response thereto; sensing theposition of the second locking element with the second Hall-effectsensor and responsively producing a second sensor signal in responsethereto; and operating the first and second switches in response to thefirst and second sensor signals, respectively, to control powerdistribution through the sensor circuit so as to affect a magnitude ofan output current produced by the sensor circuit.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a schematic view of an exemplary motor vehicle drivetrainincluding a differential assembly constructed in accordance with theteachings of the present disclosure;

FIG. 2 is a fragmentary perspective view of a front driving axle of FIG.1;

FIG. 3 is a fragmentary perspective view of the front driving axle ofFIG. 1;

FIG. 4 is an exploded perspective view of a differential assembly ofFIG. 1;

FIG. 5 is an end view of the differential assembly of FIG. 1;

FIG. 6 is a cross-sectional side view of the differential assembly takenalong line 6-6 of FIG. 5;

FIG. 7 is a fragmentary side view of the differential assembly of FIG. 1showing the actuating ring in a position disengaged from the side gear;

FIG. 8 is a fragmentary side view of the differential assembly of FIG. 1showing the actuating ring in a position drivingly engaged with the sidegear;

FIG. 9 is a fragmentary perspective of a second embodiment differentialassembly constructed in accordance with the teachings of the presentdisclosure;

FIG. 10 is a schematic depicting a circuit including a second embodimentsensor assembly in accordance with the teachings of the presentdisclosure;

FIG. 11 is a plot showing magnetic field density as a function ofdistance for a first embodiment sensor assembly;

FIG. 12 is a plot showing magnetic field density as a function ofdistance for a second embodiment sensor assembly;

FIG. 13 is a schematic illustration depicting a circuit constructed inaccordance with the teachings of the present disclosure, the circuithaving a two wire, dual sensor arrangement that is identified as SensorConfiguration 1;

FIG. 14 is a schematic diagram depicting another power transmissiondevice constructed in accordance with the teachings of the presentdisclosure;

FIG. 15 is a plot showing magnetic field density as a function ofdistance for a dual Hall sensor arrangement operating in a singlemagnetic field per Sensor Configuration 1;

FIG. 16 is a table depicting the output of the circuit of FIG. 13 basedon the operational state of the sensors;

FIG. 17 is a schematic depicting an alternate circuit constructed inaccordance with the teachings of the present disclosure and identifiedas Sensor Configuration 2;

FIG. 18 is a plot showing magnetic field density as a function ofdistance for Sensor Configuration 2;

FIG. 19 is a table depicting the output of the circuit of FIG. 17;

FIG. 20 is a schematic depicting an alternate circuit constructed inaccordance with the teachings of the present disclosure and identifiedas Sensor Configuration 3;

FIG. 21 is a plot showing magnetic field density as a function ofdistance for Sensor Configuration 3;

FIG. 22 is a table depicting the output of the circuit of FIG. 20;

FIG. 23 is a schematic depicting an alternate embodiment circuitidentified as Sensor Configuration 4;

FIG. 24 is a plot showing magnetic field density as a function ofdistance for Sensor Configuration 4;

FIG. 25 is a table depicting the output of the circuit of FIG. 23;

FIG. 26 is a schematic depicting an alternate circuit constructed inaccordance with the teachings of the present disclosure and identifiedas Sensor Configuration 5;

FIG. 27 is a plot showing magnetic field density as a function ofdistance for Sensor Configuration 5;

FIG. 28 is a table depicting the output of the circuit of FIG. 26;

FIG. 29 is a schematic depicting an alternate circuit constructed inaccordance with the teachings of the present disclosure and identifiedas Sensor Configuration 6;

FIG. 30 is a plot showing magnetic field density as a function ofdistance for Sensor Configuration 6;

FIG. 31 is a table depicting the output of the circuit of FIG. 29;

FIG. 32 is a plot showing magnetic field density as a function ofdistance for Sensor Configuration 6 where the Hall elements areprogrammed to have overlapping operational magnetic field ranges;

FIG. 33 is a table depicting the output of Sensor Configuration 6 havingoperational switch points as defined in FIG. 32;

FIG. 34 is a plot showing magnetic field density as a function ofdistance for a circuit constructed according to Sensor Configuration 6where the Hall effect sensors operate within dual magnetic fields;

FIG. 35 is a table depicting the output of the circuit according toSensor Configuration 6 and FIG. 34;

FIG. 36 is a plot showing magnetic field density as a function ofdistance for a circuit constructed according to Sensor Configuration 6operating in dual magnetic fields where the operational magnetic fielddensity ranges of the Hall effect sensors overlap; and

FIG. 37 is a table depicting the output of the circuit according toSensor Configuration 6 operating under the parameters defined by FIG.36.

DETAILED DESCRIPTION

The present disclosure is directed to an improved differential with alocking state detection system for a drivetrain of a motor vehicle. Thedifferential of the present disclosure includes an actuator operable toplace the differential in an “open” or “locked” condition. The detectionsystem provides a signal indicating whether the differential is in the“open” or “locked” condition. It should be appreciated that thedifferential of the present disclosure may be utilized with a widevariety of driveline components and is not intended to be specificallylimited to the particular application described herein. In addition, theactuator of the differential of the present disclosure may be used inconjunction with many types of differentials such as those having abevel gear design or a parallel-axis helical design which may be of anopen or limited-slip variety.

With reference to FIGS. 1-3, a drivetrain 6 for an exemplary motorvehicle is shown to include an engine 8, a transmission 10, a transfercase 12, a forward propeller shaft 14 and a rearward propeller shaft 16.Rearward propeller shaft 16 provides torque to a rear axle assembly 18.Forward propeller shaft 14 provides torque from engine 8 to a pinionshaft 20 of a front axle assembly 22. Front axle assembly 22 includes anaxle housing 24, a differential assembly 26 supported in axle housing 24and a pair of axle shafts 28 and 30 respectively interconnected to leftand right front wheels 32 and 34.

Pinion shaft 20 has a pinion gear 36 fixed thereto which drives a ringgear 38 that is fixed to a differential case 40 of differential assembly26. Differential case 40 is rotatably supported in axle housing 24 by apair of laterally spaced bearings 41. Bearings 41 are retained bybearing caps 42 coupled to axle housing 24. A gearset 43 (FIG. 4)supported within differential case 40 transfers rotary power fromdifferential case 40 to axle shafts 28 and 30, and facilitates relativerotation (i.e., differentiation) therebetween. Thus, rotary power fromengine 8 is transmitted to axle shafts 28 and 30 for driving frontwheels 32 and 34 via transmission 10, transfer case 12, forwardpropeller shaft 14, pinion shaft 20, differential case 40 and gearset43. While differential assembly 26 is depicted in a front-wheel driveapplication, the present disclosure is contemplated for use indifferential assemblies installed in trailing axles, rear axles,transfer cases for use in four-wheel drive vehicles and/or any otherknown vehicular driveline application.

FIGS. 4-8 depict differential assembly 26 to include differential case40 and gearset 43. Gearset 43 includes a pair of pinion gears 44rotatably supported on a cross shaft 45. First and second side gears 46and 47 are drivingly interconnected to pinion gears 44 and axle shafts28 and 30. Differential assembly 26 also includes an actuator and sensorassembly 48 operable to selectively couple first side gear 46 todifferential case 40, thereby placing differential assembly 26 in afully locked condition.

A cap 49 is coupled to differential case 40 to define a pocket 50 forreceipt of actuator and sensor assembly 48. Actuator and sensor assembly48 includes a solenoid assembly 52, an actuating ring 54, a draw plate56, a retainer 58 and a sensor assembly 59. Cap 49 includes a flange 60coupled to a flange 62 of case 40. Flange 60 of cap 49 includes a recess64 sized to receive a portion of solenoid assembly 52 during actuation.Cap 49 includes a pair of stepped bores 66 and 68 which define pocket50. Specifically, first bore 66 includes an annular surface 70 whilesecond bore 68 includes an annular surface 72. First bore 66 includes anend face 74 radially inwardly extending from annular surface 70. Anaperture 76 extends through the cap 49 and is in communication withsecond bore 68 where aperture 76 and second bore 68 are sized to receivea portion of the axle shaft.

Actuating ring 54 includes a generally hollow cylindrical body 78 havingan annular recess 80 formed at one end. Side gear 46 includes asimilarly sized annular recess 82 formed on an outboard face 84. Acompression spring 85 is positioned between actuating ring 54 and sidegear 46 within annular recesses 80 and 82. A plurality of axiallyextending dogs 86 protrude from an end face 88 of actuating ring 54. Acorresponding plurality of dogs 90 axially extend from outboard face 84of side gear 46. Actuating ring 54 is moveable from a disengagedposition as shown in FIGS. 6 and 7 to an engaged position shown in FIG.8. In the disengaged position, dogs 86 of actuating ring 54 are releasedfrom engagement with dogs 90 of side gear 46. In contrast, whenactuating ring 54 is moved to its engaged position, dogs 86 engage dogs90 to rotatably fix side gear 46 to differential case 40.

Solenoid assembly 52 includes a metallic cup 94 and a wire coil 96. Wirecoil 96 is positioned within cup 94 and secured thereto by an epoxy 98.Cup 94 includes an inner annular wall 100, an outer annular wall 102 andan end wall 104 interconnecting annular walls 100 and 102. Retainer 58is a substantially disc-shaped member having an outer edge 106 mountedto end wall 104 of cup 94. A portion of retainer 58 is spaced apart fromend wall 104 to define a slot 108.

Retainer 58 includes a pair of axially extending tabs 109 positionedproximate to bearing cap 42. Tabs 109 restrict rotation of retainer 58relative to axle housing 24. Sensor assembly 59 is mounted to retainer58. Sensor assembly 59 includes a Hall element 110 having asubstantially rectangular body. Hall element 110 includes a first face112 extending substantially perpendicularly to the axis of rotation ofaxle shafts 28 and 30. Sensor assembly 59 also includes a pair of wires114 extending from Hall element 110 that end at terminals 116 mountedwithin a connector 118. Connector 118 includes a body 120 extendingthrough an aperture 122 formed in axle housing 24. The ends of the wireon wire coil 96 terminate at terminals 124 mounted within connector 118.In this manner, electrical connection to solenoid assembly 52 and sensorassembly 59 may be made from outside of axle housing 24.

A target 126 includes a bracket 128, a magnet 130 and a fastener 132.Bracket 128 includes a first leg 134 having an aperture 136 extendingtherethrough. Fastener 132 extends through aperture 136 and is used tomount target 126 to bearing cap 42. Bracket 128 includes a second leg138 positioned at a right angle to first leg 134. Second leg 138 issubstantially planar and positioned substantially parallel to first face112 of Hall element 110. Magnet 130 is a substantially cylindricaldisk-shaped member mounted to second leg 138. Accordingly, magnet 130includes an outer surface 139 (shown in FIG. 7) positioned substantiallyparallel to first face 112. One skilled in the art will appreciate thatthe sensor and magnet may be re-oriented 90 degrees to the orientationshown in the Figures. As such, the orientation of sensor and magnetshown in the drawings is merely exemplary and should not limit the scopeof the disclosure.

Draw plate 56 is positioned within slot 108 defined by retainer 58 andis coupled to actuating ring 54 via a plurality of fasteners 140. Awasher 142 is positioned between cap 49 and actuating ring 54.Preferably, washer 142 is constructed from a non-ferromagnetic materialso as to reduce any tendency for actuating ring 54 to move toward endface 74 of metallic cap 49 instead of differential case 40 duringenergization of solenoid assembly 52. A bearing 144 supports cup 94 onan outer journal 146 of cap 49.

Coil 96 is coupled to a controller 148 (FIG. 1) that operates toselectively energize and de-energize coil 96. During coil energization,a magnetic field is generated by current passing through coil 96. Themagnetic field causes actuator and sensor assembly 48 to be drawn towardflange 60 of cap 49. As solenoid assembly 52 enters recess 64, dogs 86of actuating ring 54 engage dogs 90 of side gear 46. Once the dogs areengaged, actuating ring 54 is in its engaged position and differentialassembly 26 is in a fully locked condition as shown in FIG. 8. In thefully locked position, the Hall element 110 encompassed in sensorassembly 59 is spaced apart from outer surface 139 of magnet 130 by adistance “X.” At distance “X,” magnet 130 generates a predeterminedmagnetic field density. Sensor assembly 59 outputs a signal indicativeof the axial position of actuating ring 54. This signal is used bycontroller 148 as verification that differential assembly 26 is in afully locked position.

One skilled in the art will appreciate that the axially moveableelectromagnet of the present disclosure provides a simplified designhaving a reduced number of components. Additionally, the presentdisclosure utilizes the entire differential case as the armature for theelectromagnet. This allows a more efficient use of the availablemagnetic force. These features allow a designer to reduce the size ofthe electromagnet because the armature more efficiently utilizes theelectromotive force supplied by the electromagnet. Such a compact designallows for minor modification of previously used components andpackaging with a standard sized axle housing.

To place differential assembly 26 in the open, unlocked condition,current is discontinued to coil 96. The magnetic field ceases to existonce current to coil 96 is stopped. At this time, compression in spring85 causes actuator and sensor assembly 48 to axially translate anddisengage dogs 86 from dogs 90. Accordingly, side gear 46 is no longerdrivingly coupled to differential case 40, thereby placing differentialassembly 26 in the open condition shown in FIG. 7. When differentialassembly is in the open, unlocked condition, Hall element 110 ispositioned substantially closer to target 126 than when differentialassembly 26 was in the locked position. Specifically, first face 112 isspaced apart from outer surface 139 of magnet 130 a distance “Y” whencoil 96 is not energized. At distance “Y,” the magnetic field densitygenerated by magnet 130 is significantly greater than the field densityat distance “X.” Sensor assembly 59 is configured to output a signal tocontroller 148 indicating that actuating ring 54 is at a position wheredogs 86 are disengaged from dogs 90 and the differential is in an opencondition. It should also be appreciated that actuation and deactuationtimes are very short due to the small number of moving componentsinvolved. Specifically, no relative ramping or actuation of othercomponents is required to cause engagement or disengagement of dogs 86and dogs 90.

Electronic controller 148 controls the operation of actuator and sensorassembly 48. Electronic controller 148 is in receipt of data collectedby a first speed sensor 150 and a second speed sensor 152 as shown inFIG. 1. First speed sensor 150 provides data corresponding to therotational speed of axle shaft 28. Similarly, second speed sensor 152measures the rotational speed of axle shaft 30 and outputs a signal tocontroller 148 indicative thereof. Depending on the data collected atany number of vehicle sensors such as a gear position sensor 154, avehicle speed sensor 156, a transfer case range position sensor or abrake sensor 158 as shown in FIG. 1, controller 148 will determine if anelectrical signal is sent to coil 96. Controller 148 compares themeasured or calculated parameters to predetermined values and outputs anelectrical signal to place differential assembly 26 in the lockedposition only when specific conditions are met. As such, controller 148assures that an “open” condition is maintained when events such asanti-lock braking occur. The “open” condition is verified by the signaloutput from sensor assembly 59. Limiting axle differentiation duringanti-lock braking would possibly counteract the anti-lock brakingsystem. Other such situations may be programmed within controller 148.

FIG. 9 depicts a second embodiment differential assembly 160.Differential assembly 160 is substantially similar to differentialassembly 26. For clarity, like elements have been identified withpreviously introduced reference numerals. Differential assembly 160differs from differential assembly 26 in that a coil 162 is rotatablymounted on differential case 40 in a fixed axial position. Ananti-rotation bracket 164 interconnects a cup 166 with the axle housing24 (FIG. 3) to restrict coil 162 from rotation. A bearing 167 rotatablysupports cup 166 to allow the differential case 40 to rotate relative tothe coil 162 during operation of the differential assembly.

Through the use of a stationary coil 162, power supply and sensor wirerouting complexities may be reduced because the wires no longer need toaccount for axial movement of the coil. As such, coil 162 does notaxially translate nor rotate during any mode of operation ofdifferential assembly 160. An axially moveable armature 168 is coupledto actuating ring 54. Armature 168 is shaped as an annular flat ringpositioned proximate coil 162. Armature 168 and actuating ring 54 aredrivingly coupled to differential case 40 and axially moveable relativeto coil 162 and differential case 40. Armature 168 and actuating ring 54are biased toward a disengaged, open differential, position shown inFIG. 9 by a compression spring as previously described in relation todifferential assembly 26.

To place differential assembly 160 in a locked condition, coil 162 isenergized to generate a magnetic field. Armature 168 is constructed froma ferromagnetic material. Accordingly, armature 168 and actuating ring54 are axially displaced to drivingly engage actuating ring 54 with sidegear 46 to place differential assembly 160 in a locked condition.

While a front drive axle assembly has been described in detail, itshould be appreciated that the power transmitting device of the presentdisclosure is not limited to such an application. Specifically, thepresent disclosure may be used in rear drive axles, transaxles forfront-wheel drive vehicles, transfer cases for use in four-drivevehicles and/or a number of other vehicular driveline applications.

FIG. 10 depicts a circuit 198 having a second embodiment sensor assembly200. Sensor assembly 200 includes a first Hall element 202, a secondHall element 204 and a body 206 encompassing both of the Hall elements.Sensor assembly 200 is shaped substantially similarly to sensor assembly59. Sensor assembly 200 is positioned in communication with adifferential assembly in a substantially similar manner to sensorassembly 59. Accordingly, the description relating to the mounting ofsensor assembly 200 within the axle assembly will not be reiterated.

Due to the nature of Hall effect devices, permanent magnets and thegeneral environment in which sensor assembly 200 is required tofunction, a very large mechanical hysteresis is inherent in the system.Mechanical hysteresis in this instance is best described as the absolutedistance the sensor assembly must travel in relation to the targetmagnet in order to change its output state. The Hall effect deviceswitches state, or outputs a different signal, based on the Hall elementbeing exposed to a changing magnetic field density. The Hall effectdevice may be configured to start switching at a predetermined magneticfield density described as its operating point (Bop) and the fielddensity must change an amount equal to the inherent hysteresis (Bhys) ofthe Hall effect device in order to switch.

FIG. 11 is a graph showing magnetic field density versus distance forthe first embodiment sensor assembly 59 shown in FIGS. 4-8. As shown inFIG. 11, permanent magnet 130 generates an exponentially decaying fielddensity, measured in gauss versus the distance traveled in millimeters.For example, if Hall element 110 was programmed to switch at a Bop of 80gauss and had a Bhys of 10 gauss, Hall element 110 would initiate aswitch at 80 gauss and change its state at 70 gauss. Because a magneticfield is generated when coil 96 is energized, two distinct gauss curvesare created. The upper curve depicts the field density present when theelectromagnet of solenoid assembly 52 is energized. The lower curverepresents the magnetic field density generated by the permanent magnetalone when the coil 96 is not energized. As shown, a relatively largehysteresis is introduced into the system by operation of solenoidassembly 52. The magnitude of hysteresis introduced is by choice. Itshould be appreciated that the coil may be wired in the oppositepolarity to reduce the relative gap between the gauss curves.

In the embodiment depicted in FIG. 11, sensor assembly 59 moves from alocation where distance “Y” equals 4 mm and distance “X” equals 8 mm.Sensor assembly 59 does not output a signal indicating that thedifferential assembly is in the locked condition until sensor assembly59 reaches a distance of 7.8 mm of spacing between first face 112 andouter surface 139. During coil 96 deenergization, sensor assembly 59does not output a signal indicating that the differential assembly isunlocked until the spacing between the Hall element and the permanentmagnet is 4.8 mm. As such, a total mechanical hysteresis ofapproximately 3 mm exists with the single sensor embodiment. Dependingon the operational characteristics of the mechanical system includingsensor assembly 59, this magnitude of hysteresis may or not beacceptable.

FIG. 12 is a graph showing magnetic field density versus distance forthe second embodiment sensor assembly 200 shown in FIG. 10. To reducethe magnitude of mechanical hysteresis, Hall elements 202 and 204 ofsensor assembly 200 are configured in accordance with FIGS. 10 and 12.First Hall element 202 is set to have an operating point of 60 gausswhile second Hall element 204 is set to have an operating point of 100gauss. During operation, second Hall element 204 outputs a signalindicating that the differential assembly is in the locked conditiononce the magnetic field density reduces from 100 gauss to 90 gauss. Thiscondition occurs when the spacing between second Hall element 204 andouter surface 139 of magnet 130 is approximately 6.3 mm. Atelectromagnet deenergization, first Hall element 202 outputs a signalindicative of an open differential condition once the magnetic fielddensity changes from 50 to 60 gauss. This condition exists when firstHall element 202 is spaced from outer surface 139 a distance ofapproximately 5.6 mm. One skilled in the art will appreciate that thetotal mechanical hysteresis is now approximately 0.75 mm when using twoHall elements with different operating points.

The circuit 198 depicted in FIG. 10 includes first Hall effect sensor202 and second Hall effect sensor 204. First Hall effect sensor 202 iscoupled in series with a differential gain amplifier 232. Differentialgain amplifier 232 is coupled to the base of a current gain transistor234. A constant current source 236 is supplied to the collector leg ofcurrent gain transistor 234. The emitter leg of current gain transistor234 provides an output signal labeled as I_(OUT1).

In similar fashion, second Hall effect sensor 204 is connected in serieswith a differential gain amplifier 240. Differential gain amplifier 240is coupled to the base of a current gain transistor 242. Constantcurrent source 236 is supplied to the collector leg of current gaintransistor 242. The emitter leg of current gain transistor 242 providesan output signal labeled as I_(OUT2). Controller 148 analyzes I_(OUT1)and I_(OUT2) to determine the operating mode of differentiation as beinglocked or unlocked. When both I_(OUT1) and I_(OUT2) are low or zero,controller 148 determines that the differential is operating in thelocked mode. When I_(OUT1) and I_(OUT2) are both high or one, controller148 determines that the differential is operating in the unlocked mode.

FIG. 13 depicts an alternate embodiment dual Hall sensor circuit 300operable to output a signal indicative of the position of a moveablemember within a power transmission device. Circuit 300 may beimplemented in conjunction with the lockable differential assemblypreviously described. Furthermore, it is contemplated that circuit 300may be used in conjunction with any number of power transmissionsubsystems that include an axially moveable member.

For example, FIG. 14 shows a power transmission device 306 operable toselectively transfer torque from a first rotatable shaft 308 to a secondrotatable shaft 310. The rotatable shafts are at least partiallypositioned within a housing 311 and are selectively drivinglyinterconnected by a clutch assembly 312. Clutch assembly 312 includes aplurality of outer friction plates 314 slidably coupled to second shaft310 and a plurality of inner friction plates 316 slidably coupled toshaft 308. Outer plates 314 are interleaved with inner plates 316. Anactuator 318 is operable to axially displace an apply plate 320 suchthat a compressive force may be selectively applied to the clutch 312.The output torque of clutch 312 may be varied according to the inputforce generated by actuator 318.

A sensor assembly 322 is mounted to housing 311. A target 324 is mountedto axially moveable apply plate 320. In operation, actuator 318 isoperable to move apply plate 320 between at least three discretepositions. These positions are represented by target 324 being shown insolid line representation when apply plate 320 is at the first orreturned position where no torque is transferred through clutch 312, asecond position as denoted by target 324′ in hidden line representationand a third position shown as target 324″ also in hidden lines. Atposition 324′, actuator 318 moves apply plate 320 to take up axialclearance between outer plates 314 and inner plates 316 to place theclutch in a ready mode. At this position, clutch 312 transmits minimaltorque, if any, between shaft 308 and shaft 310. However, very slightmovement of apply plate 320 toward the clutch 312 will cause the clutchto generate a significant amount of torque in a relatively short periodof time. In this manner, torque delivery will not be delayed due to theactuator having to travel large distances to account for the clearancebetween the actuator plate and the friction plates of the clutch.

When the target is at position 324″, actuator 318 has driven apply plate320 in full engagement with clutch 312 and torque is being transferredthrough the clutch. Accordingly, it may be beneficial to construct asensor circuit operable to output signals indicating when an axiallymoveable member such as apply plate 320 is at one of three locations.Alternatively, only two locations may need to be determined if thesensor arrangement is used in a device such as differential assemblies26 or 160 because the axially moveable actuating ring 54 is typically inone of two locations. Actuating ring 54 is either in the fully returnedposition when the differential is in an open condition or the fullyadvanced position when the differential is in the locked condition.Various circuit embodiments and sensor configurations will be describedhereinafter. Depending on the sensor configuration, the circuit mayoutput signals indicating that the target is in one of two differentzones or that the target is located within one of three different zonesof linear position.

Referring again to FIG. 13, circuit 300 depicts a Sensor Configuration1. FIGS. 15 and 16 also relate to Sensor Configuration 1. Circuit 300includes a first Hall sensor 302, a second Hall sensor 304, a number ofresistors, R1, R2 and R3 as well as a diode D1 electricallyinterconnected as shown. These resistors and the diode are locatedwithin the housing of the power transmission device. A first pin 350 anda second pin 352 exit the housing at a bulkhead connector 354. First pin350 is connected to a DC power source while second pin 352 is connectedto a load resistor RL. Load resistor RL functions as a current sensingelement and provides an output signal Iout. One skilled in the art willappreciate that minimizing the number of wires, terminals, pins or otherelectrical connectors passing through the wall of the housing isbeneficial. For example, the impact on the housing structural integrityis minimized and the aperture extending through the housing may be moreeasily sealed if the size of the aperture is minimized.

FIG. 16 represents a state diagram defining the output of circuit 300based on the operational states of sensor 302 and sensor 304. The tableof FIG. 16 identifies sensor 302 as sensor 1 and sensor 304 as sensor 2.As is noted by reviewing the column labeled Sensor Iout, Configuration 1outputs 5 mA when the distance between the Hall effect sensors and thetarget is within zone 1 or 2. Both sensor 302 and sensor 304 are in theOFF state when the distance between the Hall effect sensors and thetarget is within zone 3. When both sensors are in the OFF state, Ioutequals 15 mA. Because the Hall effect sensors include inherenthysteresis, the distance at which the state of the sensor changesdepends on whether the magnetic field density is increasing ordecreasing. Accordingly, zones 1, 2 and 3 vary slightly depending on thedirection of travel of the axially moveable member. For example, sensor2 switches from the ON state to the OFF state after the magnetic fielddensity changes from Bop to Bhys. This change represents the spacingbetween the Hall effect sensor and the target as increasing at the pointof transition from zone 2 to zone 3 as shown at approximately 1.75 mm.If the Hall effect sensor is exposed to an increasing magnetic fielddensity, sensor 2 is shown to switch from the OFF to the ON state onlyafter the magnetic field density increases from Bhys to Bop. Thiscondition is shown to occur at approximately a 1.3 mm spacing as zone 3′is exited and zone 2′ is entered. As is illustrated by the graph, thebeginning of zone 3 does not exactly correspond to the ending of zone3′. This “tolerance” of the distance at which zone 2 ends and zone 3starts should be accounted for in the logic of the controller utilizingthe information output from circuit 300.

FIGS. 17-19 depict an electrical circuit 360 substantially similar tocircuit 300 but having a different topology, identified as SensorConfiguration 2. Circuit 360 includes first sensor 302 and second sensor304 wired in communication with resistors R1 and R2 as well as diode D1.The resistance value for R1 has been changed and R3 has been removed.First pin 350 and second pin 352 exit the housing of the powertransmission device as previously described. Pin 350 is coupled to a DCpower source and pin 352 is coupled to a current sensing load resistorRL. FIG. 19 includes a column labeled Sensor Iout which represents theoutput of the circuit 360 where sensor 1 has a Bop greater than the Bopof sensor 2. FIG. 19 includes another column entitled Alternate SensorIout which represents the output of circuit 360 if the operating pointsof sensors 1 and 2 were switched. One skilled in the art will appreciatethat three different current levels are provided depending on the stateof sensor 1 and sensor 2 according to the column labeled Sensor Iout.Specifically, Iout equals 5 mA when the spacing between the Hall effectsensors and the target is within zone 1. Iout equals 15 mA when thespacing between the sensors and the target is within zone 2. Iout equals21 mA when the spacing between the sensors and the target is within zone3. The versatility of the use of two programmable Hall effect sensors isillustrated by reviewing the Alternate Sensor Iout column and notingthat the same circuit may be used to provide an indication when thespacing between Hall sensors is within one of two areas. Differentsignals are output if the spacing lies within zone 1 or within zones 2or 3. Iout equals 5 mA only when sensor 1 and sensor 2 are both in theON state. Otherwise, if one or both of the sensors are in the OFF state,21 mA is output. Therefore, Sensor Configuration 2 is easily programmedto provide a two position sensing arrangement or a three positionsensing arrangement.

Another circuit configuration 370 is represented by FIGS. 20-22. Circuit370 or Sensor Configuration 3 is substantially similar to SensorConfigurations 1 and 2 with minor changes to the circuit. The circuitmodifications cause the magnitude of the output current levels tochange. Furthermore, different sensor state combinations providedifferent outputs. The Sensor Iout column shows that 3 mA is output inzone 1 and zone 1′ while 21 mA will be output when the spacing betweenthe sensor and the target is within zone 2, zone 2′, zone 3 or zone 3′.

FIGS. 23-25 relate to Sensor Configuration 4 having a circuit 380. FIGS.26-28 correspond to Sensor Configuration 5 having a circuit 390. FIGS.29-31 depict Sensor Configuration 6 having a circuit 395. Each of theseconfigurations is substantially similar to Sensor Configurations 1-3previously described in detail. As such, like elements will retain theirpreviously introduced reference numerals. Sensor Configurations 4, 5 and6 further illustrate the versatility of the present disclosure byconstructing simple circuits using two Hall elements to output signalsindicative of the position of an axially moveable component within apower transmission device.

FIGS. 32 and 33 depict a method of adjusting the width of certaindetection zones by modifying the operating switch point of one sensorrelative to the other. The embodiments previously described included afirst sensor having an operating range of magnetic field density definedby its operating point and its hysteresis switch point. The operatingrange of sensor 1 is spaced apart from the operating range of magneticfield density of sensor 2 because sensor 2 is purposefully configuredwith different operating and hysteresis switch points. In the embodimentdepicted in FIG. 32, Sensor Configuration 6 is shown to include theoperating switch point of sensor 2 being programmed to lie within theoperating range of magnetic field density defined by sensor 1.Specifically, sensor 2 has an operating point (Bop) that is greater thanthe hysteresis switch point (Bhys) of sensor 1 but lower than theoperating switch point (Bop) of sensor 1. By setting the operatingswitch points of the two Hall effect sensors relatively closelytogether, the axial travel defined by zone 2 is greatly reduced. Asdepicted in FIGS. 32 and 33, the distance traveled to exit zone 1, passentirely through zone 2 and enter zone 3 is approximately 0.5 mm.Accordingly, the dual Hall sensor arrangement having overlappingoperating ranges may be useful for an application where relatively smallaxial distances are traveled by the axially moveable member.

FIGS. 34-37 illustrate that any one of the Sensor Configurations 1-6 mayalso be used in a dual field operation mode. These Figures alsoillustrate that the operating ranges of the Hall sensors may beoverlapped or not overlapped in the dual field mode of operation as wellas the single field mode of operation. The dual field operation mode wasdescribed in greater detail previously in reference to the lockabledifferential having an electromagnet with a coil operable to generate anelectromagnetic field. However, in this embodiment the polarity of thepermanent magnet and the electromagnet are positioned such that themagnetic field density at the sensors decreases when the electromagnetcoil is on.

Furthermore, the foregoing discussion discloses and describes merelyexemplary embodiments of the present disclosure. One skilled in the artwill readily recognize from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications and variationsmay be made therein without department from the spirit and scope of thedisclosure as defined in the following claims.

1. An apparatus for transferring power comprising: a first powertransmitting element; a second power transmitting element; a housing; afirst locking element received in the housing and coupled to the firstpower transmitting element; a second locking element received in thehousing and coupled to the second power transmitting element, the secondlocking element being axially movable along a rotational axis aboutwhich the first and second locking elements are rotatably disposed suchthat the second locking element is movable between a first position, inwhich rotary power is not transmitted between the first and secondlocking elements, and a second position in which rotary power istransmitted between the first and second locking elements; and a sensorcircuit in the housing, the sensor circuit having a first Hall-effectsensor and a second Hall-effect sensor that are configured to sense anaxial position of the second locking element, the sensor circuitproducing a single analog output current indicative of a sensed axialposition of the second locking element.
 2. The apparatus of claim 1,wherein the first Hall-effect sensor is configured to switch between afirst switch state and a second switch state at a first predeterminedmagnetic field density and wherein the second Hall-effect sensor isconfigured to switch between a third switch state and a fourth switchstate at a second predetermined magnetic field density.
 3. The apparatusof claim 2, wherein the first and second predetermined magnetic fielddensities are different.
 4. The apparatus of claim 3, wherein the firstHall-effect sensor has a hysteresis of a first magnitude associated withthe switching of the first Hall-effect sensor from the second switchstate to the first switch state, where the second Hall-effect sensor hasa hysteresis of a second magnitude associated with the switching of thesecond Hall-effect sensor from the fourth switch state to the thirdswitch state, where the first predetermined magnetic field density andthe first magnitude establish a first range of magnetic field densities,wherein the second predetermined magnetic field density and the secondmagnitude establish a second range of magnetic field densities andwherein the first range of magnetic field densities intersects thesecond range of magnetic field densities.
 5. The apparatus of claim 3,wherein the first Hall-effect sensor has a hysteresis of a firstmagnitude associated with the switching of the first Hall-effect sensorfrom the second switch state to the first switch state, where the secondHall-effect sensor has a hysteresis of a second magnitude associatedwith the switching of the second Hall-effect sensor from the fourthswitch state to the third switch state, where the first predeterminedmagnetic field density and the first magnitude establish a first rangeof magnetic field densities, wherein the second predetermined magneticfield density and the second magnitude establish a second range ofmagnetic field densities and wherein the first range of magnetic fielddensities does not intersect the second range of magnetic fielddensities.
 6. The apparatus of claim 1, wherein the single analog outputcurrent produced by the sensor circuit is transmitted out of the housingvia a single wire.
 7. The apparatus of claim 6, further comprising acurrent sensor coupled to the wire.
 8. The apparatus of claim 1, whereina magnitude of the single analog output current toggles between a firstcurrent value and a second current value based at least partly on aswitching state of each of the first and second Hall-effect sensors. 9.The apparatus of claim 8, further comprising a solenoid having a coilthat is energized to initiate movement of the second locking elementalong the rotational axis, wherein the magnitude of the single analogoutput current is also based on an energization state of the coil. 10.The apparatus of claim 8, wherein the magnitude of the single analogoutput current switches between at least three predetermined currentlevels based at least partly on the switching state of each of the firstand second Hall-effect sensors.
 11. The apparatus of claim 1, whereinthe sensor circuit includes a first switch and a second switch, thefirst switch being operated based on a switching state of the firstHall-effect sensor, the second switch being operated based on aswitching state of the second Hall-effect sensor.
 12. The apparatus ofclaim 11, wherein the first switch comprises a first transistor and thesecond switch comprises a second transistor.
 13. The apparatus of claim12, wherein each of the first and second transistors includes a base, anemitter and a collector, and wherein a first electric load is coupled tothe first transistor across the emitter and the collector of the firsttransistor, and wherein a second electric load is coupled to the secondtransistor across the emitter and the collector of the secondtransistor.
 14. The apparatus of claim 13, wherein the first electricalload is different from the second electrical load.
 15. The apparatus ofclaim 13, wherein the emitter of the first transistor is coupled inseries to the collector of the second transistor.
 16. The apparatus ofclaim 13, wherein the collectors of the first and second transistors arecoupled in parallel to a voltage source and wherein the emitters of thefirst and second transistors are coupled in parallel.
 17. The apparatusof claim 1, wherein the apparatus comprises a clutch or a differential.18. A method of detecting an operating mode of a power transfer devicethat is configured to transmit rotary power, the power transmittingdevice having a first power transmitting element, a second powertransmitting element, a housing, a first locking element received in thehousing and coupled to the first power transmitting element, a secondlocking element received in the housing and coupled to the second powertransmitting element, and a sensor circuit having first and secondHall-effect sensors and first and second switches, the second lockingelement being axially movable along a rotational axis about which thefirst and second locking elements are rotatably disposed such that thesecond locking element is movable between a first position, in whichrotary power is not transmitted between the first and second lockingelements, and a second position in which rotary power is transmittedbetween the first and second locking elements, the method comprising:fixedly coupling the first and second Hall-effect sensors to one of thesecond locking element and the housing; fixedly coupling a magnet to theother one of the second locking element and the housing; sensing aposition of the second locking element with the first Hall-effect sensorand responsively producing a first sensor signal in response thereto;sensing the position of the second locking element with the secondHall-effect sensor and responsively producing a second sensor signal inresponse thereto; and operating the first and second switches inresponse to the first and second sensor signals, respectively, tocontrol power distribution through the sensor circuit so as to affect amagnitude of an output current produced by the sensor circuit.
 19. Themethod of claim 18, wherein the first and second switches are first andsecond transistors, respectively, and wherein the first and secondsensor signals are employed to control the flow of current through thefirst and second transistors.